The present invention relates to an ink ejection recording apparatus and, more particularly, to such an apparatus in which discharged ink droplets are accelerated by a stream of air supplied from a pressurized air source which is energized during operation of the apparatus.
The air-accelerated ink ejection apparatus disclosed in U.S. Pat. Nos. 4,106,032 and 4,301,460 includes an ink ejecting unit having a liquid chamber to which ink is supplied from a liquid container and an air chamber provided forwardly of the liquid chamber and axially aligned discharge channels for discharging ink therethrough into the atmosphere when the pressure inside the liquid chamber is increased rapidly by means of a piezoelectric transducer mounted adjacent to the liquid chamber in response to electrical drive signals applied thereto. The air chamber is constantly supplied with pressurized air from a pressure source when the apparatus is in operation to provide a stream of air that accelerates the discharged ink droplets onto a writing surface. The pressurized air is also supplied to the liquid container so that there is established a static balance between the pressure in the air and liquid chambers. This results in lowering of the minimum operating voltage of the apparatus and ensures that the reproduced image has a minutely changing gradation.
An ink ejection apparatus has been proposed and used which employs a plurality of ink ejection apparatus described above. The ink ejection apparatus has a plurality of ink tanks and ink ejection heads corresponding to the respective ink tanks. In this ink ejection apparatus, it is necessary to equalize the static pressures applied to the ink nozzles of all ink ejection heads. To this end, hitherto, the ink ejection heads and the ink tanks are arranged such that the differences in height between the ink ejection heads and the levels of ink in the associated ink tanks are equalized. With this arrangement, the static ink pressures applied to the ink nozzles of all the ink ejection heads, thus providing an equal condition for jetting of the ink.
This solution, however, cannot be applied to the case where a plurality of ink ejection heads which are arranged at different heights are connected to a common ink tank. For the purpose of attaining a high printing speed, it has been proposed to install a multiplicity of ink ejection heads, e.g., three ink ejection heads for each of yellow, magenta, cyan and black colors which amounts to 12 heads in total. In order to equalize the static ink pressures acting in all the ink ejection heads, it is necessary to install ink tanks of the same number as the ink ejection heads. Since the space available for the installation of these ink tanks is limited, the volume of each tank has to be reduced, with the result that the frequency of supply of the ink to each tank is increased undesirably. In addition, the system as a whole is so complicated that the reliability of operation of the system is impaired undesirabily. It is to be pointed out also that the cost of the system as a whole is raised due to the necessity for installation of sensors on all the ink tanks for the purpose of sensing the amounts of ink remaining in these ink tanks.